Update documentation

Issue: SPR-13471

Author: snicoll

src/asciidoc/core-beans.adoc

@@ -6788,8 +6788,12 @@ work on the configuration class itself since it is being created as a bean insta
 	@Configuration
 	public class RepositoryConfig {
 
+		private final DataSource dataSource;
+
 		@Autowired
-		private DataSource dataSource;
+		public RepositoryConfig(DataSource dataSource) {
+			this.dataSource = dataSource;
+		}
 
 		@Bean
 		public AccountRepository accountRepository() {
@@ -6817,6 +6821,14 @@ work on the configuration class itself since it is being created as a bean insta
 	}
 ----
 
+[TIP]
+====
+Constructor injection in `@Configuration` classes is only supported as of Spring
+Framework 4.3. Note also that there is no need to specify `@Autowired` if the target
+bean defines only one constructor; in the example above, `@Autowired` is not necessary
+on the `RepositoryConfig` constructor.
+====
+
 .[[beans-java-injecting-imported-beans-fq]]Fully-qualifying imported beans for ease of navigation
 --
 In the scenario above, using `@Autowired` works well and provides the desired

src/asciidoc/whats-new.adoc

@@ -631,6 +631,7 @@ public @interface MyTestConfig {
 
 * It is no longer necessary to specify the `@Autowired` annotation if the target
   bean only define one constructor.
+* `@Configuration` classes support constructor injection.
 
 
 === Testing Improvements